1. Field of the Invention
The present invention relates to a sheet conveying apparatus having a structure to convey a sheet from a first conveying path to a second conveying path which are mutually merged, and more specifically, relates to the sheet conveying apparatus enabling to reduce noise at the time of sheet conveyance from the first conveying path to the second conveying path and an image forming apparatus including the sheet conveying apparatus.
2. Description of the Related Art
Recently, with an image forming apparatus such as a copying machine, noise caused by a sheet itself occurring during sheet conveyance becomes striking according to gradual reduction of operation noise. For example, a top end of a sheet S to be conveyed from a conveying path 30 causes top end hitting noise when being abutted to a vertical conveying path 45 at a merging section (i.e., a curved portion) where the conveying path 30 and the conveying path 45 are at a right angle, as illustrated in FIG. 12A. Further, as illustrated in FIG. 12B, a rear end of the sheet S causes rear end bounce noise as being abutted to a guide face of the conveying path 45 when reaching the merging section after passing through the conveying path 30.
In the related art, to solve such a noise problem, there has been known an image forming apparatus which reduces noise caused by abutment of a sheet conveyed through a sheet conveying path by arranging a flexible sheet such as mylar (registered trademark) at a merging section where two sheet conveying paths are merged (see Japanese Patent Laid-open No. 11-043238).
However, with the above structure in which sheets are abutted to the flexible sheet, since top ends and rear ends of sheets are abutted to the same part of the flexible sheet repeatedly for each sheet, there is a possibility of losing capability of sheet conveyance owing to scrape or breakage of the flexible sheet with use.
Further, there has been known an image forming apparatus having a structure to reduce noise occurring when a sheet conveyed from a first pair of rollers at the upstream side is abutted to a merging section on a midstream toward a second pair of rollers at the downstream side in a curved sheet conveying path (see U.S. Patent Application Publication No. 2009/0026691 A1). In the image forming apparatus, a guide plate having holes formed and having sound absorbing material fixed at a back face thereof is arranged at the merging section (i.e., a curved portion).
However, with the above structure in which holes are formed at the sheet conveying path and the sound absorbing material is arranged at the back face thereof, it is difficult to obtain a sufficient effect of noise reduction as a result of that a face to which a sheet is directly abutted is formed of a rigid member such as a metal plate. Here, a member having low rigidity for noise reduction can be utilized. However, since durability is decreased when a low rigidity member is utilized, it has been difficult to satisfy both of high noise reduction performance and durability.
Meanwhile, there has been proposed an apparatus including mutually-merged first and second sheet conveying paths and a belt conveying portion which is moved to guide sheets to the second sheet conveying path with a structure to enhance noise reduction performance by abutting top ends and rear ends of sheets to the belt conveying portion (see U.S. Patent Application Publication No. 2007/0057444 A1).
The above apparatus includes the first conveying path which conveys a sheet with a first conveying portion, the second conveying path which conveys a sheet with a second conveying portion as being merged to the first conveying path at the downstream side, and the belt conveying portion which cushions abutment of a sheet as being arranged at the second conveying path.
Incidentally, with the apparatus enhancing noise reduction performance by abutting top ends and rear ends of sheets to the belt conveying portion, the first conveying portion includes split-like rubber drive rollers formed of a roller body separated in plural in an axial direction as a drive roller. Here, since the split-like rubber drive rollers arranged at the belt conveying portion in an opposed manner are abutted to a rubber-made endless belt at the belt conveying portion, sheets are to be nipped by the rubber-made roller body and the rubber-made endless belt. Accordingly, frictional charging difference becomes large between a nipped part and an un-nipped part of a sheet owing to the roller body and the endless belt which are made of rubber. That is, charges are kept at the sheet as a result of frictional charging of the sheet at the nipped part between the roller body and the endless belt while few charges are kept at the un-nipped part. In an image forming apparatus of an electrophotographic system, a toner image is transferred to a sheet by applying transfer bias to a transfer portion. Therefore, when frictional charging difference occurs on the sheet, there is a possibility to cause imaging instability. Accordingly, it is not preferable to perform nipping and conveying with a conveying member causing contact of rubber to an image transfer face of a sheet.
To address the above issues, the present invention provides a sheet conveying apparatus having a structure not to cause imaging failure while enabling to reduce noise occurring at a curved portion of a conveying path of which conveying direction is varied and an image forming apparatus including the sheet conveying apparatus.